Photoelectric sensors debuted as throughbeam devices composed of lights and reflectors. Over the years, these sensors have developed into a multitude of designs, each used for a variety of purposes. One of these designs is the self-contained throughbeam, sometimes called a fork sensor. This sensor style, typically configured in a block letter C-shape, sends an electromagnetic signal (e.g., a beam of visible light, a laser beam, etc.) across from one arm of the sensor to another. Self-contained fork sensors can be used for a variety of applications, such as in production lines. For example, the sensors can be used to detect the presence or absence of items passing through the beam along a conveyor.
FIG. 1 illustrates a schematic of a fork sensor 100 currently used in industry. Housing 110 of the fork sensor 100 includes a first and second arm 101, 102 extending from a base 105. The first arm 101 includes an emitter 107 at a distal end 103. A second arm 102 includes a receiver 108 at a distal end 104. The emitter 107 is connected to a power source (not shown) and the receiver 108 is connected to a signal processing assembly (not shown). The emitter 107 is aligned with the receiver 108 such that a beam of light transmitted by the emitter 107 is received by the receiver 108 and converted into an electrical signal output. Placing a sufficiently opaque object between the emitter 107 and the receiver 108 interrupts a portion of the transmitted light before it reaches the receiver 108, thereby changing the signal output.
The beam of light has an effective width W1, which is defined by the amount of light transmitted by the emitter 107 that is also received by the receiver 108. The magnitude of the effective width W1 depends on the size of the emitter 107 and the receiver 108. Generally, both the emitter 107 and the receiver 108 are on the order of a couple millimeters wide. Therefore, the effective width W1 of the beam is only on the order of a couple millimeters.
In order for an object to interrupt the beam as it passes between the emitter 107 and the receiver 108, at least a portion of the object must pass within those few millimeters. Therefore, movement of smaller objects through the fork sensor 100 must be accurately controlled.